<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>变量</title>
    <script>
        var a = 1;
        //alert(a)

        document.write(a+'------'+typeof(a)+'<br>');

        var b = +"123abc";
        document.write(typeof(b)+'<br>');
        document.write(b+1+"<br>");
        var c = 3;
        document.write(1/3);
        document.write(!c);
        var sum = 0;
        
    </script>
</head>
<body>

</body>
</html>